1. Field of the Invention
The present invention relates to a semiconductor device and a method of manufacturing the device, particularly to a semiconductor device having a capacitor using a dielectric and a method of manufacturing the device.
2. Description of the Related Art
In a ferroelectric random access memory (FeRAM) which is a nonvolatile memory utilizing a ferroelectric thin film, a capacitor portion of a DRAM is replaced with a ferroelectric material, and the memory is expected as the next-generation memory.
In the FeRAM, a ferroelectric thin film of PZT (Pb(ZrxTi1−x)O3), BIT (Bi4Ti3O12), SBT (SrBi2Ta2O9) or the like is used for the capacitor portion. All of the films have a crystal structure based on a perovskite structure including an oxygen octahedron as a basic structure. These materials are different from a conventional Si oxide film in that ferroelectricity which is a characteristic is not developed in an amorphous state, and therefore cannot be used. Therefore, steps for crystallization, for example, crystallization thermal treatment at a high temperature, in-situ crystallization process at a high temperature and the like, are required. In general, a temperature of at least 400 to 700° C. is required for the crystallization depending on the material. As a film forming method, there are an MOCVD method, a sputtering method, and a chemical solution deposition (CSD) method.
Although the characteristics of an FeRAM capacitor utilizing the above-described ferroelectric material after forming a capacitor film are satisfactory, there has been a problem that step damage by diffusion of H or the like is incurred in subsequent steps such as an RIE step, interlayer film forming step, wiring step, and sintering, and in a process at a molding time, and capacitor characteristics are deteriorated.
Then, a protective film is used in order to reduce the damage in the post steps with respect to the capacitor. In Jpn. Pat. Appln. KOKAI Publication No. 2001-36026, a capacitor cell is described in which an Al oxide film is utilized as a protective film in a capacitor upper layer portion to thereby avoid damage.
On the other hand, as a structure of a capacitor, with high integration, development of an offset type in which the upper electrode of the capacitor is connected to an active region of a transistor to a capacitor-on-plug (COP) type in which the capacitor is disposed on a plug in order to prepare an FeRAM having a higher density has been advanced in recent years. In this COP type, a plug structure formed of W or Si connected from an active region of the transistor is disposed right under the capacitor, and the cell size can be reduced in the same manner as in a stacked capacitor of a DRAM.
However, in this structure, there has been a problem that a plug material disposed right under the capacitor is oxidized, contact resistance increases, and peeling occurs in a worst case in heat treatment under an oxygen-containing atmosphere for recovering damage. To avoid this problem, barrier layers such as TiAlN, TiN, TaSiN are formed, and electrode materials such as IrO2, Ir, RuO2, Ru have been tried.
However, in this case, since the structure is complicated, and the height of the capacitor increases, a problem occurs that the above-described protective film is not easily attached to the side wall of the capacitor. To solve the problem, in Jpn. Pat. Appln. KOKAI Publication No. 2002-43541, as a method of manufacturing an Al oxide film which is the protective film of the capacitor, an atomic layer deposition (ALD) method having a high step-coating property is used. An example of use of the ALD method is described in U.S. Pat. No. 6,144,060.
However, since trimethyl-aluminum (TMA) having a high reducing property is used in a source gas in the ALD method, which is one type of CVD method, there is a problem that the capacitor characteristics are deteriorated at the time of the film formation.